QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 908A
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
1
LTC3773EG
DESCRIPTION
Demonstration circuit 908A is a Polyphase 3-
Output Step-Down Supply with Tracking featuring
the LTC3773EG. The output voltages are 3.3V,
2.5V and 1.8V and the maximum load current for
each is 15A. The input voltage range is 7V to 24V.
Typical applications include s
ervers, communica-
tions, computers and industrial power supplies.
The board can be programmed for either continu-
ous-conduction mode (CCM), pulse skip mode
(DCM) or Burst Mode (BM). Other features of the
board include an SDB pin which can be used for
rail sequencing, a phase mode pin, and a dynamic
load circuit for each rail.
An on-board LT1933 (5V / 500mA buck converter)
provides current for the LTC3773EG’s internal
logic and gate drive circuitry. The 5V bias can also
be supplied externally. If an external bias voltage
is applied it needs to be between 4.5V and 7.0V.
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
7V
Maximum Input Voltage
24V
V
OUT1
V
IN
= 7V to 24V, I
OUT
= 0A to 15A
3.3V ±3%
V
OUT2
V
IN
= 7V to 24V, I
OUT
= 0A to 15A
2.5V ±3%
V
OUT3
V
IN
= 7V to 24V, I
OUT
= 0A to 15A
1.8V ±3%
Typical output voltage ripple for VOUT1
VIN = 12V, IOUT1 = 15A, 20MHz BW
25mVp-p TYP
Typical output voltage ripple for VOUT2
VIN = 12V, IOUT2 = 15A, 20MHz BW
25mVp-p TYP
Typical output voltage ripple for VOUT3
VIN = 12V, IOUT3 = 15A, 20MHz BW
25mVp-p TYP
Nominal Switching Frequency
220kHz TYP
Efficiency
(see Figure 4 for typical efficiency curves)
V
IN
= 12V, V
OUT1
= 3.3V, I
OUT1
= 15A
V
IN
= 12V, V
OUT2
= 2.5V, I
OUT2
= 15A
V
IN
= 12V, V
OUT3
= 1.8V, I
OUT3
= 15A
92.2% TYP
90.9% TYP
88.9% TYP
